you're cooking the pecans during the recipe, so using roasted pecans would leave them too dry by the end of the recipe. but you can probably used pre-roasted pecans and toss them in about a minute before you pull the rest out of the oven, so the pecans just warm up a bit but don't dry out.

Or, if you're asking if you must use pecans at all, you don't. You can substitute pretty much any other raw nut (raw for the reasons mentioned above), or you can increase the amount of seeds and coconut.